. 6, DIG0~DIG5 and DP are respectively the column lines and row line ports of the six keys which achieve keyboard monitoring, decoding and key codes identification. F. Alarm Circuit In order to simplify the circuit and convenient debugging, a5V automatic buzzer is used in the alarm circuit [8]. And this make the software programming simplified. As shown in Fig. 7, it is controlled by the PNP transistor 9012 whose base is connected to the pin P2.5 of the AT89 C51. When the temperature exceeds the upper and lower limit value, the P2.5 output low level which makes the transistor beon and then an alarm is given by the buzzer. G. Drive Circuit A step motor is used as the drive device to control the temperature. The four-phase and eight-beat pulse distribution mode is used to drive motor and the
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